Ferromagnetic compositions of iron, rhodium and at least one other element of atomicnumbers 21-25 and 27-30



United States Patent FERROMAGNETIC COMPOSITIONS OF IRON, RHO- DIUM AND AT LEAST ONE OTHER ELEMENT 0F ATOMIC NUMBERS 21-25 AND 27-30 Paul H. L. Walter, Wilmington, DeL, assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Mar. 5, 1962, Ser. No. 177,230

6 Claims. (Cl. 75-122) This invention relates to, and has as its principal object the provision of, new magnetic materials useful for the interconversion and control of various forms of energy.

Magnetic materials, inclusive of both ferroand ferrimagnetic materials, are broadly old and many such compositions are known. Similarly, many energy transducer devices based thereon are also known. However, the previously known ferromagnetic compositions suffered variously from one or more inferior properties, qualities, or behavior. For instance, many of the ferromagnetic compositions did not exhibit as high saturation magnetization values as was desired for many outlets, nor did they exhibit sufficient corrosion, oxidation, or high temperature resistance. While some of these ferro-, ferrimagnetic compoistions did exhibit the rather peculiar property of an abrupt and large-scale increase in saturation magnetization with increasing temperature, those previously known either exhibited this so-called exchange inversion temperature at relatively low temperature and/ or suffered from having too low a Curie temperature for successful application in many desired embodiments.

The iron/ rhodium binary alloys of, for instance, Fallot, Revue Scientifique, 77, 498 (1939), and Kouvel et al., General Electric Research Report No. 61-RL-2870M, November 1961, also exhibited this abrupt increase in saturation magnetization with increasing temperature with a a of about 112 gauss cm. /g., i.e., 112 emu./g., as measured in a 5,000 oersteds (or conventionally a 5 kOe.) magnetic field, but at a temperature of only 350 K. (i.e., about 77 C.). Furthermore, the temperature at which the material suddenly changes from antiferromagnetic to ferromagnetic could not be widely varied without increasing greatly the ratio of residual magnetization to maximum magnetization.

There has now been discovered a new class of ferriferromagnetic materials which exhibit very good saturation magnetization values and high Curie temperaturetures. These compositions are also outstanding in corrosion and oxidation resistance and thermal degradation, properties in which many or most of the presently known magnetic compositions are found wanting.

A particularly preferred subclass of these new magnetic materials exhibits a maximum saturation magnetization within a restricted temperature range and a very much smaller saturation magnetization at temperatures above and below this range. These preferred magnetic compositions exhibit a relatively low saturation magnetization at low temperatures which abruptly increases with increasing temperature, at a specific temperature range for each composition, to a maximum saturation magnetization many orders of magnitude greater than that exhibited at temperatures below this critical temperature range. This maximum saturation magnetization slowly decreases with increasing temperature until the Curie temperature is reached. On being cooled from the Curie temperature these preferred compositions exhibit slowly increasing magnetization with decreasing temperature until a maximum saturation magnetization value is reached and then abruptly exhibit a large decrease in saturation magnetization, reaching ultimately a low remanence saturation magnetization.

The maximum sat- 3,140,942 Patented July 14, 1964 iCC uration magnetization is generally the same on decreasing temperature as that achieved on increasing temperature. However, the temperature at which the maximum value is exhibited is somewhat lower on a decreasing temperature cycle than an increasing temperature cycle, i.e., there is magnetization hysteresis as a function of cycling temperature.

Not only is this subclass of the magnetic compositions of this invention preferred, but also devices for the interconversion and control of various forms of energy based on this preferred class of magnetic compositions comprise another preferred portion of the present invention. Another preferred embodiment of the invention is directed to methods for preparing these preferred magnetic products exhibiting these novel magnetic properties, and also to the preparation of energy transducers broadly based on such products.

These superior magnetic compositions consist essentially of iron. and rhodium in major proportion and at least one other member of the first long transition period of the Periodic Table of the elements of atomic number 21-30 inclusive, viz., scandium, titanium, vanadium, chromium, manganese, cobalt, nickel, copper, and zinc. The iron and rhoduim will normally be present in substantially equal atomic proportions, but not necessarily equal since either may exceed the other by 20 atomic percent. It is always necessary that both iron and rhodium be present. The at least one other metal of the first long period of the transition metals running from atomic number 21 through atomic number 30, which also must always be present, will range in amount from 0.01-0.20 atom proportion. Thus, the new superior magnetic compositions of the present invention are of the formula wherein M represents a transition metal of atomic number 21-30 inclusive other than iron; x is an integer from one to six, and generally one to two; a and b, which can be alike or different, are numbers ranging from 0.8-1.2; and c is a number ranging from 0.01-0.20 and in the instance when x22, the requisite cs can be alike or different but still must fall in the indicated range. The subscript numbers a, b, and 0 refer to the atom proportions of the respective elements in the products. M can be different within the same defined group when x is greater than 1.

The proportions of metals within the alloys of this invention can be expressed in somewhat different terminology as follows: iron, about 33.33-59.70 atom percent; rhodium, about 33.33-59.70 atom percent; and other transition element or elements of atomic numer 21-30, i.e., elements of atomic number 21-25 and 27-30, about 20.0-0.415 atom percent. It is to be distinctly understood that at least one of the transition elements of atomic number 21-30 other than iron is comprised within the designated 200-0415 atom percent and that up to six of such elements can be present.

The following examples in which the parts given are by weight are submitted to illustrate the present invention further and not to limit it.

EXAMPLE I An intimate mixture of 1.0854 parts of iron, 2.0000 parts of rhodium, and 0.0954 part of cobalt, all in finely divided form, was placed in a die and pressed into a pellet. The pellet was dropped into an aluminum oxide crucible which was then placed inside the heating element of a carbon-resistance furnace. A bell jar was placed over the furnace which was then evacuated and heated to 840 C. Argon was admitted into the bell jar until the pressure in the furnace was 0.6 atmosphere. The temperature of the furnace was then increased until the metal pellet had visibly melted (about 1600 C.). The is present in the alloys Fe and Rh in major amount and metal pellet was held in the molten state for five minutes, a minor amount of one other transition element of the after which the temperature was gradually reduced over first transition period, but is also inclusive of those alloy a period of 28 minutes at which time the furnace was compositions consisting essentially of Fe and Rh in major turned off at an approximate internal temperature of 5 amount and relatively minor amounts of more than one 300 C. The crucible was removed from the furnace, and transition element from the first long period of the tranthe Fe/Rh/0.0833 Co alloy slug removed. sition metals of the Periodic Table. Thus, the present To guarantee homogeneity, the metal slug was sealed invention is also specifically inclusive of four, five, six, in an evacuated silica tube and heated at 950 C. for 70 seven, eight, etc., element-containing alloys wherein the hours, after which it was cooled slowly to room tem- Fe and Rh are always present and in major amount, and perature over a period of 24 hours. After this annealing the other elements are present in minor amount and are treatment, the slug superficially and physically appeared all members of the first long transition period of the unchanged. It exhibited a saturation magnetization of Periodic Chart of the elements. Thus, to be specific, the 144.9 emu./g. at 269 C. and a Curie temperature present invention also includes the following multicomof 480 C. ponent magnetic alloys:

For brevity, the additional detailed examples illust Fe /Rh C .05, n.s 1.2 0.05 0.05 tive of the present invention are covered in the following P h /M /c i table in which these new magnetic compositions were Few/R111 2/Cu005/Zn0.05,

prepared as described in full detail in Example I in the F /Rh /S /Ti /Z /cr foregoing with the indicated variations in charge com- Fe /Rh /Sc /T uns o.1o oios position, preparation temperature, time required to re- Fem/Rh1 2/S0 05/Ti0I05/ZI1O 02/Cro 02/Mn0 02/Co0 02/ duce furnace temperature to permlt removal of the charge, Niom, and the like" and, finally, the annealing time and the resultant different magnetic properties. As in Example I, in all in- While varying modifying amounts of the other transition stances the charge was held in the molten state at the elements of the first long Period can he Present in these indicated preparative temperature for five minutes. In new alloys which have Fe and Rh in major amount and this table the charged compositions are in the indicated two or more of the Said other transition elements, atomic proportions. The annealing time was, in all inerahy Speaking there Will he a total of 110 more han 0 2 stances, at 950 C., and the symbol T refers t th to 0.4 atom proportion of said other modifying transition temperature at which the indicated new magnetic com elements 111 y One y position undergoes the rapid and 1arge scale change in The novel Compositions of the present invention saturation magnetization. The column T (heating) lists a maximum Saturation magnetization at temperatures in the temperatures at which such a phenomenon occurs as the range to +3750 ahd Curie tefhperathres the sample is raised frorn a lower temperature and the in the range +300 t0 +500 C. Thfi magnetic Com- Column headed TS (cooling) indicates the temperature positions also exhibit increasing saturation magnetization at which the sample undergoes the abrupt large-scale Withihereasihg temperature ihatelhpefature range below decrease in saturation magnetization on cooling from a the Chile P higher temperature. The symbol T is used to represent Sheh Compositions are useful in devices Operating at h C i temperatum h Symbol am is used to i temperatures near room temperature and even at eledicate the residual saturation magnetization of the sample. Vated temperature for those exhibiting IIlaXimum Satur- The symbol a is used to indicate the maximum saturaation hlaghetizatiohs in the higher temperature rangestion magnetization of the material, and the column headed Those exhibiting maximum Saturation magnetization at temp.-o' i di t h temperature t hi h thi ivery low temperatures are especially useful in devices such mum saturation magnetization value is attained. In all as refrigerators d temp rat re-sensitive Controls operinstances in all columns involving temperature the units ating at temperatures near the boiling point of liquid are in C, The t r ti magnetization d t were helium and below. The manner in which saturation obtained using a magnetic field of 15,75 16 0() 1 0 (L magnetization varies with temperatures can be controlkiloersteds or 15,750 16,000 er t d led by modifying the composition of the ferromagnetic Table I Prep. Time to Anneal Composition Temp, Reduce Time, Heat- 0001- Tu (Tl-cs 'mnx TemIL-amu degrees Temp, hrs. ing Ts iug Ts Fe/Rh/0.0833:

Ni 1, s15 14 Suitable specific compositions within the scope of the products. The most outstanding compositions exhibit present invention, i.e, those materials consisting essena very low residual magnetism below the lower ferrotially of Fe, Rh, and at least one other transition elemagnetic transition temperature. ment from the first long period of the transition metals These novel magnetic compositions are prepared by of the Periodic Chart of the elements running from heating mixtures of the elements or compounds of the atomic number 21 through and inclusive of 30, include elements to a temperature in the range from 600 to 2500 C. or higher as equipment and va or ressure Fe/Rh/S,F 11/, g z f f vigg vig limitations dictate within the normal practice. Temper- 0.9 1.1 0.1 0.8 1.2 0.1 0.9 1.0 0.01, f 700 t C d f 1200 t 7 0 Fe /Rh /Co Fe /Rh /Ni Fe /Rh /Ni a an mm 0 are 0.9 1.0 0.1 1.2 0.8 0.05: 1.0 1.1 0.05, u u 11 1 d T t f 1 b 1 0 0 9 0 5 P61 0 /Rh1 2 /Ni Fe /Rh /Cu 5 a y emp oye empera ures 0 at east a out 1550-1600 C are enerall necessar 1f th e F6 o/Rh o/ZH 1. g Y y OmPOSl trons are to be melted. The time of heatmg is not critits stated in the foregoing, the present invention is not ical but should be sufiicient to permit complete reaction l mlted composition-wise to three-component composiof the ingredients. Heating times ranging up to about tions similar to those just speclfically named wherein there 50 hours for the lower tmperature ranges are necessary to effect appreciable solid state reaction. Longer times can be useful in some cases, particularly, for instance, if it is desired to prepare the composition in single crystal form. Generally speaking, the most efficient technique in the sense of obtaining the most complete reaction is to carry out the reaction in the melt for time periods of from at least to about 60 minutes or longer.

Heating can be carried out at atmosphereic pressure with the reactants protected by a blanket of inert gas such as helium or argon. Alternatively, the reaction can be conducted in an evacuated vessel. It is also possible to employ superatmospheric pressure. The reaction can also be carried out in sealed vessels under the autogenous pressure developed by the reaction mixture at the reaction temperatures. Since the preferred techniques involve effecting reaction in the melt, it is normally preferred to carry out the reaction in inert refractory materials under reduced pressure or under a protective blanket of an inert gas.

The materials employed in preparing these new compositions can be the elements themeslves or any of the binary or ternary combinations thereof as called for by the desired stoichiometry. Thus, to prepare Fe/Rh/Sc the three elements themesleves can be charged or the necessary Fe/ Rh binary can be separately prepared previously and then mixed with the requisite amount of Sc and reaction effected to form the desired ternary composition. In any event, it is preferred that the materials be in powder or granular form and that they be well mixed before heating is commenced.

The starting materials are employed in such relative amounts that the resulting mixture contains the desired proportions of Fe/Rh and the requisite transition metal or metal. Thus, to prepare an Fe /Rh /Cr the respective elements or binaries are charged in the indicated relative atomic proportions.

After the desired preparative heating cycle has been completed, the reaction mixture is cooled and, if desired, subjected to purification, e.g., by extraction with acids or, after grinding, by magnetic separation. This first cooling cycle will be relatively rapid.

To assure the greatest homogeneity in the product and the maximum ferromagnetic behavior, it has been found that the products should preferably be annealed by holding for a relatively long time at an elevated temperature and then slowly cooling to room temperature over a controlled temperature profile, e.g., by a suitably programed or recorder driven furnace. Thus, it is preferred that the products of the present invention after the preparative heating and cooling cycle, whether or not any intervening mechanical, chemical, or magnetic purification is effected, be heated to an elevated temperature in the range 800-l000 C. or higher and held at this temperature for relatively long periods of time, e.g., from 50 to 100 hours or so, in an inert atmosphere, i.e., under evacuated conditions or with a protective blanket of an inert gas such as argon or helium. Then, the compositions of the present invention are further annealed carefully by final slow cooling from this temperature to room temperature over a period of approximately 24 hours.

The novel magnetic compositions of this invention exhibit several magnetic characteristics which make them especially valuable for use in various specific applications. The novel lower ferromagnetic transition temperature is a distinguishing feature conferring unusual utility on these materials. Particularly outstanding are the relatively high saturation magnetization values exhibited by these compositions, as well as the high Curie temperature and good values of saturation magnetization exhibited at the maximum with increasing temperature below the Curie temperature. All the compositions are extremely resistant to corrosion, oxidation, and exhibit good magnetic behavior at elevated temperatures.

The preferred products are useful in devices for the interconversion and control of various forms of energy such as solar motors, temperature-sensitive inductors, thermally activated clutches, and temperature compensators in devices based on conventional magnetic material where sagging of magnetic properties with increas ing temperature is functionally deleterious. In their essential features all of these devices comprise at least three components, viz., the magnetic component described previously, suitable means for applying a form of energy to and from the magnetic component, and suitable means for utilizing the output from the magnetic component. For some applications, the devices of the present invention can include means for controllably magnetizing and demagnetizing the magnetic component. At temperatures within the ferromagnetic range, these compositions can be used in any of the conventional applications for ferromagnetic materials for which their properties render them suitable, e.g., electromagnets, high-frequency coil cores, information and memory storage elements, and the like.

In the preferred devices the elements which provide heat to or remove heat from the magnetic element, which magnetize and demagnetize the magnetic element, and which collect and detect the new form of energy produced are conventional in the art. For example, by introducing a pivotal element, with a magnetic component as just described, in a magnetic field and having means for magnetizing the magnetic component, the pivotal element can be caused to move in said field. In this way, mechanical work can be done. The pivotal element can be an armature, an oscillating arm, or a metering device.

The new magnetic compositions of the present invention are useful as the active component in forming temperature responsive electrical inductors comprising, usually in combination, a metallic core consisting at least in part of one of the present magnetic compositions with or without a second material exhibiting a magnetic permeability which is substantially invariant with temperature, and an electrical conductor wrapped around said core. These temperature responsive electrical (magnetic) inductors are widely useful in any circuits in which inductance is a significant parameter. Thus, these inductors based on the present magnetic compositions can be employed as an element of the frequency-determining circuit of a sine-wave oscillator or as a high-temperature safety device to reduce circuti current with increasing temperature or as a current-controlling device in which the control current flows through a heater winding on the temperature-sensitive inductor. In addition, these temperature-responsive inductors can be used in conjunction with a wide variety of conventional core materials, including both the metallic and oxide types, representative of which latter are, for example, the ferrites.

In view of the increasing saturation magnetization with increasing temperature below the Curie temperature, the new magnetic materials of the present invention are useful in forming temperature responsive magnetically operated rotary force couplings comprising, in combination, a pair of relatively rotatable elements to be coupled disposed adjacent to one another in a common magnetic flux path, a permanent magnet, and one of the new magnetic compositions of the present invention which exhibits a changing permeability accompanying a reversible first order transition from a first solid state phase to a second solid state phase at a given temperature, both disposed in said common magnetic flux path, the permanent magnet and the magnetic composition of the present invention completing a magnetic flux circuit between the said elements of the pair coupling one of the elements with the other in that temperature range when the magnetic composition of the present invention exists in a first solid state phase and uncoupling the elements of the pair as the temperature decreases when the suben a es 6 stance exists in a second solid state phase, and obviously the reverse and in cycles.

The new magnetic compositions of the present invention are also useful in thermomagnetic devices as the working substance therein, said devices being useful for effecting heat transfer, i.e., serving as heat pumps, e.g., a refrigerator. These new magnetic compositions in such devices in view of the first order solid phase to solid phase transition with changing temperature with accompanying relatively large change in internal energy content in going through the transition will function as the said working substance in said devices with allied coupled magnetic means for cyclically inducing said transition in a direction such to lower the temperature of the substance when one solid state phase is attained and to increase the temperature when the other solid state phase is attained along with an allied heat source and a thermal sink relative to one of the solid state phases individually adapted to effect heat transfer sequentially with respect to said substance.

With respect to the thermomagnetic working capability of the present magnetic compositions, they are of particular interest in the formation of gradient objects comprising the said magnetic materials varying in composition angularly about a point or axis or varied along one or more selected lines, which need not be straight, in the said gradient object such as to display the first order solid phase to solid phase transition at successively higher temperatures in a first path or a direction along or about said point or axis or said line, and at successively lower temperatures in an opposite path or direction achieved by varying the composition of the magnetic alloys. These gradient objects are particularly useful in many kinds of energy-converting devices, e.g., as temperature indicators, cores in temperature-sensitive inductors, transformers, elements in thermal switches, and the like, and are particularly outstanding because of the possible ready and precise adjustment of device operation achievable to suit particular environmental conditions obtained with the great control possible through the narrow compositional changes.

These new magnetic materials are also useful as the working substance in a method of information storage and retrieval wherein a recording member containing one of the new magnetic compositions of this invention substantially homogeneously distribtued therethrough is exposed to a read-in beam, modulated patternwise in accordance with information to be stored from a temperature variation inducing component, thereby establishing in the said recording member regions of relatively higher and relatively lower intrinsic magnetization corresponding to said information, maintaining said elelnent after said read-in at a temperature within the thermal hysteresis range, and reading out the stored information by exposing the element at said temperature to a low intensity electron beam Whereby deviations in said beam corresponding to the stored information are produced and converted into electrical signals. Intrinsic magnetization is used here as defined by Cusack, The Electrical and Magnetic Properties of Solids, Longmans-Green & Company, London, 1958, page 315.

The first order solid phase to solid phase transition accompanied by thermal hysteresis which is exhibited by the new magnetic materials is characterized by abrupt change not only in the magnetic properties but also in a number of the other physical properties of the materials and any of these properties can be employed in any sensing or read-out method. Thus, after modulated read-in, read-out can be based on the change in electrical resistance of the new magnetic materials serving as the Working substance of said recording member simply by providing read-out means sensitive to changes in resistance. Alternatively, read-out can be based upon changes in a linear dimension or in a volume of the working substance as desired.

Because of their outstanding magnetic properties coupled with good stability to temperature, atmosphere, corrosion, oxidation, and the like, and particularly because of the relatively high Curie temperatures that they possess, the preferred magnetic materials are broadly outstanding as the working substances in various devices whereby, generically, magnetic energy is changed controllably to mechanical, electrical, or thermal energies; mechanical energy is converted controllably into electrical, magnetical, or thermal energies; or thermal energy is controllably converted to mechanical, magnetic, or electrical energies.

More specifically, the magnetic compositions of the present invention can serve as the working substances in magnetic switches, radiation-intensity meters, reciprocating engines, devices for maintaining constant temperature difference between two zones, magnetic balances, thermomagnetic generators, solar motors, temperature indicators, image-forming components, magnetic flashers, variable resistors, differential transformers, temperature responsive resonators, and the like.

Since obvious modifications and equivalents in the invention will be evident to those skilled in the chemical arts, I propose to be bound solely by the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An alloy in which (A) iron, (B) rhodium, and (C) at least one transition element of atomic number 21- 25 and 27-30 are present in the atom proportions 0.8 to 1.2 of (A), 0.8 to 1.2 of (B), and 0.4 to 0.01 of (C).

. An alloy of claim 1 in which (C) is cobalt.

3. An alloy of claim 1 in which (C) is nickel. 4. An alloy of claim 1 in which (C) is copper. 5. An alloy of claim 1 in which (C) is chromium. 6. An alloy of claim 1 in which (C) is manganese.

References Cited in the file of this patent Hansen: Constitution of Binary Alloys, 2nd edition, McGraw-Hill, 1958, pages 702703. 

1. AN ALLOY IN WHICH (A) IRON, (B) RHODIUM, AND (C) AT LEAST ONE TRANSITION ELEMENT OF ATOMIC NUMBER 2125 AND 27-30 ARE PRESENT IN THE ATOM PROPORTIONS 0.8 TO 1.2 OF (A), 0.8 TO 1.2 OF (B), AND 0.4 TO 0.01 OF (C). 